1. Field of the Invention
The present invention relates to integrated circuit (IC) cards and related systems. More particularly, the present invention relates to an IC card and an IC card system having suspend/resume functions.
2. Description of the Related Art
IC cards enjoy increasing popularity, come in a number of different form factors, and employ varying technologies to store and communicate data. So-called smart cards which use a memory circuit to store data, as opposed to conventional credit/debit cards which use a magnetic strip, are one class of IC cards. Memory cards, generally employed as a portable storage medium, are another class of IC cards. Conventional memory card includes SM (Smart Media) cards, SD (Secure Digital) cards, CF (Compact Flash) cards, XD cards, MS (Memory Stick) cards, and MMC (MultiMedia) cards.
Recent advancements in semiconductor integration technology have generally reduced the overall size of the memory devices mounted on IC cards while at the same time providing expanded storage capacity. The security features associated with the conventional IC cards are also markedly improved.
IC cards typically operate in response to a sequence of commands received from a “host device”, such as a computer system, a transaction terminal, and/or a card reader. Various commands within the sequence of commands have differing importance or priority within the context of the host device/IC card interactions. For example, a host device may transmit a first command to an IC card, and immediately thereafter begin executing an operation that results in a second command to be sent to the IC card. Where the second command has a higher priority than the first command being processed by the IC card, the host device will forcibly interrupt execution of the first command, and thereafter transmit the second command to the IC card for execution. Once the second command has been executed, the host device transmits the first command to the IC card for execution.
Historically, the foregoing command sequence causes the IC to throw out or flush a number of so-called “assets” related to the first command. Assets include, data structures, data values, intermediate results, scratch pad values, temporary files, register values, data flags, variable values, and similar items that are used, defined, stored or transferred during the receipt, execution, and resolution of a command. Many, if not all, of these assets are flushed when the IC card receives the interrupt caused by the second command.
However, after the second command has been executed and the first command is again received from the host device, the IC card must begin the operations related to the first command from scratch. That is, the assets associated with the first command must be completely recreated regardless of their prior state just before the interrupt. This drawback significantly impairs the rate of command throughput for the IC card system.